A rainwater tank buyers guide

A rainwater tank is one of the best ways to become more water self-sufficient, but which tank is right for your home? Lance Turner looks at the options.

Rainwater tanks come in almost any size, shape and colour you can imagine, with a variety of materials to suit different preferences or usage requirements. So what should you look for when buying a tank?

The first decision you have to make is where the tank will be located. Where you place the tank will determine its size and shape, and possibly even its colour if it needs to blend into the surrounding vegetation or dwelling walls. A large yard offers a number of options. You could place it next to the house or shed, or even under the house.

You also need to consider how the water will get from the roof into the tank, as well as overflow piping. However, there are a number of different systems for plumbing a tank to a home’s gutters that allow a tank to be situated some distance from the home, so this should probably not be an overriding consideration.

Tank materials

The six most common rainwater tank materials are concrete, fibreglass, plastic (usually polyethylene, often just called ‘poly’, or PVC, used in flexible bladder tanks), Aquaplate Colorbond (thin sheet steel with a colour coating on the outside and a waterproof coating on the inside), galvanised steel and stainless steel. Each of these materials has advantages and disadvantages, so let’s look at a few of those.

Durability

A water tank can be a considerable expense, even after a rebate, so you want it to last as long as possible. The expected lifetime of any tank should be at least 20 years, and indeed, many tanks come with a 20 or even 25 year warranty. However, a number of factors will determine just how long the tank actually lasts, and that includes water quality, maintenance and positioning of the tank.

For example, plastic tanks are relatively immune to damage from salty water, so if your tank is regularly topped up from a bore or dam, then a plastic tank might be the best solution. However, if your tank only needs to hold rainwater, then any tank material should be suitable.

The tank’s location can affect the lifetime of the materials. Ideally, the tank should be located in shade if possible, not just to keep the water temperature low and reduce evaporation, but also because some materials are degraded more rapidly by direct sunlight.

Most poly tanks will slowly degrade over time with exposure to the sun, despite having UV inhibitors added to the plastic. Because the plastic is being used to hold water, there are limits to how much UV inhibitor and other chemicals can be added to the polyethylene, so eventually the tanks will suffer some degradation.

Metal tanks come in three common materials. Corrugated galvanised steel tanks have been popular in both rural and urban situations for a long time.

Another steel tank type, Aquaplate, is a derivative of Colorbond steel. It has the colour coating on one side and a waterproof coating designed specifically for tank manufacture on the other. Provided the coating is not damaged during the tank manufacturing process and seams are correctly formed and sealed, the tank should last a great many years.

Stainless steel tanks are known for their durability and strength. They are generally small modular tanks for urban use, but large stainless steel tanks are also available. These are made from corrugated stainless steel that looks much like corrugated iron, just a lot shinier. While stainless steel tanks can be more expensive than other types, they have a number of advantages which we will look at later.

Concrete tanks can be quite durable, but they do tend to sweat if they don’t have a plastic or rubber liner. If you look at a concrete tank that has been around for a while, it is not uncommon to see white powdery ‘salt’ residue on the outside.